While the effectiveness of intravenous thrombolysis (IVT) decreases over time, patients show considerable variability in how quickly their ischemic core progresses. Quantitative net water uptake (NWU) has emerged as a biomarker indicating blood-brain barrier disruption and may better reflect the "tissue clock" than time alone. Low NWU is associated with favorable outcomes, whereas high NWU predicts poor outcomes and futile recanalization. The study aims to determine whether NWU measured on initial non-contrast CT is a treatment effect modifier for the IVT therapy.

Inclusion Criteria:

• Acute ischemic stroke treated with intravenous thrombolysis
• Imaging with non-contrast cranial CT on admission
• Follow-up imaging with non-contrast cranial CT or MRI 12-24 hours after IVT
• Final Infarct volume > 5ml
• ASPECTS available

Exclusion Criteria:

• Known use of oral anticoagulation (OAC) on admission
• Preexisting ischemic infarction on admission non-contrast cranial CT
• Patients with large vessel occlusion AIS who underwent mechanical thrombectomy
• Low imaging quality precluding radiological measurements
• Severe white matter lesions precluding radiological measurements
• No ASPECTS

Patients aged over 18 years with acute ischemic stroke, symptom onset within 24 hours prior to admission and treatment in one of the stroke units of the participating institutions between 2018 and 2025 treated using IVT and fullfilling inclusion criteria

Individual participant data that underlie the results after deidentification

Data that support the findings of this study will be available from the corresponding author after academic board review and upon reasonable request